Regensburg 2010 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 7: SC: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence
TT 7.2: Talk
Monday, March 22, 2010, 14:15–14:30, H20
Doppler shift in Andreev reflection from a moving superconducting condensate in Nb/InAs Josephson junctions — Rohlfing Franziska1, •Tkachov Grigory1,2, Otto Florian1, Richter Klaus1, Weiss Dieter1, and Strunk Christoph1 — 1Universität Regensburg — 2Universität Würzburg
We present experimental and theoretical studies of narrow ballistic Josephson weak links in InAs quantum wells contacted by Nb electrodes and subject to an external magnetic field [1]. We find a dramatic magnetic-field suppression of the Andreev reflection amplitude, which occurs even for in-plane field orientation with essentially no magnetic flux through the junction. Our observations demonstrate the presence of a Doppler shift in the energy of the Andreev levels, which results from diamagnetic screening currents in the hybrid Nb/InAs banks. The data for conductance, excess and critical currents can be consistently explained by taking into accout the field- and geometry-dependent phase gradient of the superconducting order parameter and the McMillan energy, characterizing the proximity effect in the Nb/InAs banks. Our analysis suggests that a similar Doppler shift in Andreev reflection should, generally, be expected in other 2D hybrid systems such as, e.g., graphene-superconductor Josephson links [2].
[1] F. Rohlfing et al., Phys. Rev. B 80(R) (2009).
[2] H. B. Heersche et al., Nature 446, 56 (2007).